This invention relates to coating compositions for abrasive backings and particularly to those compositions containing an aminoplast resin and a thermoplastic resin.
Coated abrasives generally comprise a flexible backing upon which a binder holds and supports a coating of abrasive grains. The backing can be selected from paper, cloth, film, vulcanized fiber, etc., or a combination of one or more of these materials. The abrasive grains can be formed of flint, garnet, aluminum oxide, alumina-zirconia, ceramic aluminum oxide, diamond, silicon carbide, and the like. Binders are commonly selected from phenolic resins, hide glue, urea-formaldehyde resins, urethane resins, epoxy resins, and varnish. Phenolic resins include those of the phenol-aldehyde type.
Coated abrasives may employ a make coat of resinous binder material in order to secure the abrasive grains to the backing, and a size coat of resinous binder material can be applied over the make coat and abrasive grains in order to more firmly bond the abrasive grains to the backing. The resinous material of the make and size coats may be the same material or may be different materials. A common resinous material used for both make and size coatings is generically referred to as phenolic resin. Phenolic resins are a class of materials made from the reaction of phenol with various aldehydes.
Phenolic resins are commonly used in coated abrasive articles because of their high adhesive strength to abrasive particles, durability, and high thermal stability. There are two types of phenolic resins, resole and novolac. Resole phenolic resins have a molar ratio of formaldehyde to phenol greater than or equal to one to one, typically between 1.5:1.0 to 3.0:1.0. Novolac resins have a molar ratio of formaldehyde to phenol less than one to one.
The phenolic resins contain about 70 percent to about 85 percent solids, and preferably contain about 72 percent to about 82 percent solids. If the percent solids is very low, then more energy is required to remove the water and/or solvent. If the percent solids is very high, then the viscosity of the resulting phenolic resin is too high which leads to processing problems. The remainder of the phenolic resin is preferably water with substantially no organic solvent due to environmental concerns with the manufacturing of substantially no organic solvent due to environmental concerns with the manufacturing of abrasive articles. Examples of commercially available phenolic resins include those known under the trade designations VARCUM and DUREZ, available from Occidental Chemical Corp., Tonawanda, N.Y.; AROFENE and AROTAP, available from Ashland Chemical Company, Columbus, Ohio; RESINOX, available from Monsanto, St. Louis, Mo.; and BAKELITE, available from Union Carbide, Danbury, Conn.
Although phenolic resins are widely used in the coated abrasives industry, phenolic resins do not adhere well to some types of backing materials. Poor adhesion may cause the phenolic binder to peel away or shear off prematurely as the abrasive article is subjected to normal use. This lack of adhesion limits the types of backings that can be used in coated abrasive articles that use phenolic resin binders.
In one aspect, the invention provides a treated substrate for an abrasive article. The treatment coat, also called a xe2x80x9cpresizexe2x80x9d is made from a binder precursor or curable composition comprising an oligomeric aminoplast resin having on average at least one pendant xcex1,xcex2-unsaturated carbonyl group per oligomeric unit, a thermoplastic polyamide, and a catalyst for crosslinking or curing the xcex1,xcex2-unsaturated functionality of the aminoplast resin.
In another aspect, the invention provides a substrate for an abrasive article comprising a) a backing; and b) a crosslinked treatment coat on said backing, said treatment coat is formed from a curable precursor composition comprising a mixture of i) from about 30 to about 60 weight percent of an oligomeric aminoplast resin having on average at least one pendant xcex1,xcex2-unsaturated carbonyl group per oligomeric unit, ii) from about 70 to about 40 weight percent of a thermoplastic polyamide miscible in said aminoplast resin, the weight percents being based on the total resin content, and iii) a sufficient amount of a catalyst for the curable oligomeric aminoplast resin having on average at least one pendant xcex1,xcex2-unsaturated carbonyl group per oligomeric unit, said catalyst being stable at the temperature of mixing of the components.
In another aspect, the invention provides a curable precursor composition comprising a) from about 30 to about 60 weight percent of an oligomeric aminoplast resin having on average at least one pendant xcex1,xcex2-unsaturated carbonyl group per oligomeric unit; b) from about 70 to about 40 weight percent of a thermoplastic polyamide miscible in said aminoplast resin, the weight percents being based on the total resin content; and c) a sufficient amount of a catalyst for the curable oligomeric aminoplast resin having on average at least one pendant xcex1,xcex2-unsaturated carbonyl group per oligomeric unit, said catalyst being stable at temperature of mixing of the components.
The cured composition is also useful as a make coat, a size coat for coated abrasives, and as a laminating adhesive for multi-layer backing substrates.
In another aspect, the invention provides a treated substrate comprising a substrate which comprises a hydroenhanced cloth and a treatment coat on the substrate. xe2x80x9cHydroenhancedxe2x80x9d means that the substrate is treated using high pressure water to increase the surface area of the yarns. An example of this treatment is described in U.S. Pat. No. 4,976,456. The treatment coat may be selected from a variety of compositions suitable for use in abrasive articles.
The term xe2x80x9cprecursorxe2x80x9d means the binder is uncured and not crosslinked. The term xe2x80x9ccrosslinkedxe2x80x9d means a material having polymeric sections that are interconnected through chemical bonds (that is, interchain links) to form a three-dimensional molecular network. Thus, the binder precursor is in an uncured state when applied to the backing.
In general, the aminoplast resin/polyamide treatment coat comprises a semi-interpenetrating polymer network of a cured or crosslinked thermosetting polymer and a thermoplastic polymer. As used herein, a xe2x80x9csemi-interpenetrating polymer network (semi-IPN)xe2x80x9d is defined as a polymer network of two or more polymers wherein at least one polymer is crosslinked and at least one is uncrosslinked.
For purposes of this application, xe2x80x9ccured,xe2x80x9d xe2x80x9ccrosslinked,xe2x80x9d and xe2x80x9cpolymerizedxe2x80x9d can be used interchangeably. For purposes of this invention, a binder precursor is xe2x80x9cenergy-curablexe2x80x9d in the sense that it can crosslink (that is, cure) upon exposure to radiation; for example, actinic radiation, electron beam radiation, and/or thermal radiation. A binder precursor may be in the form of a molten mixture or may be a solid at room temperature. For instance, a binder precursor may be a solid film that is transfer coated to the backing. Upon heating to elevated temperatures, this binder precursor is capable of flowing, increasing the tack of the hot melt binder precursor, and allowing the hot melt binder precursor to penetrate and bond intimately with the backing substrate. Alternatively, for instance, if the resin is solvent-borne (organic or water), ( less than 100 percent solids) or blended with low molecular weight reactive diluents (100 percent solids), the binder precursor may be liquid at room temperature.
As used herein, a xe2x80x9chot meltxe2x80x9dcomposition refers to a composition that is a solid at room temperature (about 20 to 22xc2x0 C.) but which, upon heating, melts to a viscous liquid that can be readily applied to a backing. A xe2x80x9cmelt processablexe2x80x9d composition refers to a composition that can transform, for example, by heat and/or pressure, from a solid to a viscous liquid by melting, at which point it can be readily applied to a backing.
Desirably, the aminoplast resin/polyamide binder precursors of the invention can be formulated as solvent free systems (that is, they have less than 1 percent solvent in the solid state). However, if so desired, it may be feasible to incorporate solvent or other viscosity-reducing reactive diluents into the binder precursor.
A xe2x80x9cclothxe2x80x9d is a generic term which includes all textile fabrics or felts. A xe2x80x9cclothxe2x80x9d as used herein, may contain any of the commonly known textile fibers, natural or manmade, or a combination thereof, and which are formed by weaving, knitting, felting, needling, or other processes known in the textile industry.
A xe2x80x9ccontinuous filament yarnxe2x80x9d is a yarn comprising indefinitely long fibers such as those found in silk, or those manufactured fibers which are extruded into filaments and then assembled into a yarn with or without a twist.
The aminoplast resin/polyamide compositions of the invention combine the toughness, the improved adhesion to other resins such as phenolics, and the melt-processibilty of thermoplastic polyamides with the rapid curing, high temperature stability, and phenolic resin compatibility of the oligomeric aminoplast resins. The resulting solventless compositions are processed at moderate temperatures (220-260xc2x0 F. (104-127xc2x0 C.)) as compared with typical thermoplastic materials processed in excess of 204xc2x0 C., and thus allow the use of temperature sensitive backing materials in coated abrasives. The aminoplast resin/polyamide compositions of the invention may also be used as laminating or transfer coating adhesives in composite backings that provide strength and durability similar to that of cloth at less cost.
A preferred binder precursor of the invention contains from about 20 to about 60 weight percent of an oligomeric aminoplast resin having on average at least one pendant xcex1,xcex2-unsaturated carbonyl group per oligomeric unit and from about 40 to about 80 weight percent of thermoplastic polyamide, the weight percent being based on the total resin content of the composition. A more preferred binder precursor of the invention contains from about 30 to about 40 weight percent of an oligomeric aminoplast resin having on average at least one pendant xcex1,xcex2-unsaturated carbonyl group per oligomeric unit and from about 60 to about 70 weight percent of thermoplastic polyamide, the weight percent being based on the total resin content of the composition. A preferred catalyst for the oligomeric aminoplast resins is a free radical producing photoinitiator. The preferred aminoplast resins of the invention are acrylamidomethyl-novolac resins (AMNs).
The binder precursors of the invention preferably contain at least one oligomeric aminoplast resin having on average at least one pendant xcex1,xcex2-unsaturated carbonyl group per oligomeric unit. Aminoplast resins having at least one pendant xcex1,xcex2-unsaturated carbonyl group per oligomeric unit are made by reacting an amino compound with an aldehyde; the resulting product is then reacted with an oligomeric material. Formaldehyde is the preferred aldehyde.
Aminoplast Resins
The preferred oligomeric material is a phenol novolac resin. Typically, the phenol novolac resin is made by reacting a phenol monomer with an aldehyde in the presence of an acid catalyst, with the molar ratio of the aldehyde to phenol being less than one. Examples of aldehydes used to prepare novolacs include formaldehyde, acetaldehyde, propionaldehyde, glyoxal, and furfural. The preferred aldehyde is formaldehyde because of its availability, reactivity, and low cost. A typical phenol novolac resin is illustrated below: 
There are essentially no hydroxymethyl groups present for further condensation. Typically, these materials have a molecular weight ranging from about 300 to about 1,500. Additionally, the starting phenol monomer can be substituted with various groups such as alkyl, alkoxy, carboxyl, and sulfonic acid, so long as there are at least two reactive sites remaining to form the novolac.
Instead of using the phenol monomer, other chemicals can be reacted with the aldehyde to produce a novolac type resin. Examples of these chemicals include: cresol, xylenol, resorcinol, catechol, bisphenol A, naphthols, or combinations thereof to form a novolac resin.
To form the oligomeric aminoplast resins of this invention, the aminoplast having hydroxyalkyl groups and the oligomeric material are first combined in a reaction vessel along with an acid catalyst. Representative examples of acid catalysts include trifluoroacetic acid, p-toluenesulfonic acid, and sulfuric acid. Then, the reaction mixture is gently heated to about 30xc2x0 to 100xc2x0 C., preferably 70xc2x0 to 80xc2x0 C. to bring about any one of the following reactions: 
where R1 is as defined above; R4 represents a substituent, or combination of substituents, that does not adversely affect the reaction; R5 represents xe2x80x94OH, xe2x80x94SH, xe2x80x94NH2, hydrogen, alkylamnino group, alkylthio group, alkyl group, or alkoxy group; R6 represents an xcex1,xcex2-unsaturated alkenyl group. The alkylamino, alkylthio, alkyl, alkoxy and alkenyl groups of R5 and R6, preferably have 1 to 20 carbon atoms, inclusive. Examples of substituents suitable for R4 include hydrogen, alkyl group, preferably having 1 to 20 carbon atoms, inclusive, alkoxy group, preferably having 1 to 20 carbon atoms, inclusive, xe2x80x94OH group, mercapto group, and other groups that activate the aromatic ring toward electrophilic substitution. These types of reactions are commonly referred to as Tscherniac-Einhorn reactions.
There may be side reactions and other products formed from Reactions I through III.
Examples of the type of reaction encompassed by Reaction IV can be found in the following references: Zaugg, H. E.; W. B. Martin, xe2x80x9cAlpha-Amido alkylations at Carbonxe2x80x9d, Organic Reactions, Vol. 14, 1965 pages 52 to 77; and Hellmann, H., xe2x80x9cAmidomethylationxe2x80x9d, Newer Methods of Preparative Organic Chemistry, Vol. II, Academic Press (New York and London; 1963), pp. 277-302, both of which are incorporated herein by reference.
In Reactions I through III, the first reactant is a typical example of an oligomeric material. In the reactants in Reactions I through III, n is preferably an integer between 0 and 8, because on both sides of the n group there is a monomeric repeating unit. Thus, when these two monomeric repeating units are added to n, the total number of repeating units is between 2 and 10. Specific compounds and details of their manufacture are found in U.S. Pat. No. 5,236,472, the contents of which are incorporated herein by reference.
A preferred oligomeric aminoplast resin having on average at least one pendant xcex1,xcex2-unsaturated carbonyl group per oligomeric unit is an acrylamidomethyl-novolak resin or AMN. Useful AMNs of the invention have an average acrylamide functionality of from 0.8 to 2.5 acrylamide groups per aromatic ring. Preferred AMNs of the invention include those having an average acrylamide functionality of 1.5-2.0 acrylamide groups per aromatic ring. An even more preferred AMN has an average acrylamide functionality of 1.5 acrylamide groups per aromatic ring. Useful AMNs of the invention have a formaldehyde to phenol ratio (F/P) of from 0.25 to 1.0. The preferred F/P ratio for the AMNs of the invention is 0.5 on a molar basis. The F/P ratio is the molar ratio of formaldehyde to phenol charged in the reactor.
Thermoplastic Polyamides
Compositions of the invention also contain at least one thermoplastic polyamide. The thermoplastic polyamides of the invention are compatible with the oligomeric aminoplast resins in the melt phase. xe2x80x9cCompatiblexe2x80x9d means that the oligomeric aminoplast resin and the thermoplastic polyamide are sufficiently miscible and the melt viscocities of the oligomeric aminoplast resin and the thermoplastic polyamide are sufficiently similar such that a uniform mixture can be obtained with conventional extrusion compounding equipment. The thermoplastic polyamides of the invention have melting points that are lower than the thermal reaction temperature of the oligomeric aminoplast resins. The melting points of the thermoplastic polyamides are below the temperature required to initiate crosslinking of the oligomeric aminoplast resins. Useful thermoplastic polyamides of the invention have a melting point temperature in the range of about 95 to about 150xc2x0 C. as measured by differential scanning calorimetry (DSC). Preferred thermoplastic polyamides of the invention have a DSC melting point of about 95 to about 110xc2x0 C., and a more preferred thermoplastic polyamide has a melting point of about 103xc2x0 C.
The viscocities of the polyamides of the invention are similar to those of the oligomeric aminoplast resins of the invention at the processing temperature of the oligomeric aminoplast resin (about 104-127xc2x0 C.) Useful thermoplastic polyamides of the invention have a melt flow rate of about 10 to 90 g/10 min, preferably about 15 to 90 g/10 min, more preferably about 50 to 90 g/10 min, and even more preferably about 90 g/10 min, at a temperature of 160xc2x0 C.
Preferred thermoplastic polyamides are terpolymers produced from lactams and diamines. Preferred polyamides are made from lauryl lactam as one of the monomers. Preferred commercially available thermoplastic polyamides are terpolymers produced from lactams and diamines. The preferred commercially available thermoplastic polyamides have the trade designations VESTAMELT 732, VESTAMELT 730, VESTAMELT 742, VESTAMELT 750/751, VESTAMELT 755, and VESTAMELT 760, and are available from Creanova, Somerset, N.J.
Catalysts
The compositions of the invention contain at least one catalyst for curing the oligomeric aminoplast resin. The oligomeric aminoplast resin can be cured by heat or radiation energy. If the oligomeric aminoplast resin is cured by heat, the temperature of the oven should be set to at least about 120xc2x0 C. and held at this temperature for at least 4 hours. Curing can be effected in shorter times at higher temperatures. The temperature requirements may be lower depending upon the heat stability of the synthetic or paper backings.
If the oligomeric aminoplast resin is cured by radiation, the amount of radiation depends upon the degree of cure desired of the oligomeric aminoplast resin used in the binder. Examples of radiation energy sources include ionizing radiation, ultraviolet radiation, and visible light radiation. Ionizing radiation preferably has an energy level of 0.1 to 10 megarad, more preferably 1 to 10 megarad. Ultraviolet radiation is electromagnetic radiation having a wavelength of from about 200 to 400 nanometers. Visible light radiation is electromagnetic radiation having a wavelength of from about 400 to 760 nanometers. The rate of curing of the binder composition depends upon the thickness as well as the optical density and nature of the composition.
If the oligomeric aminoplast resin is cured by heat, a thermal initiator can be utilized to facilitate and/or enhance the rate or extent of cure. Examples of useful thermal initiators include peroxides, for example, benzoyl peroxide, azo compounds, benzophenones, and quinones.
If the binder precursor composition is to be cured by ultraviolet radiation, a photoiniator is required to initiate free radicals. Examples of such photoinitiators include organic peroxides, azo compounds, quinones, benzophenones, nitro compounds, acyl halides, hydrazones, mercapto compounds, pyrylium compounds, triacrylimidizoles, bisimidizoles, chloroalkyltriazines, benzoin ethers, benzil ketals, thioxanthones, and acetophenone derivatives. Useful commercially available photocatalysts or photoinitiators include those under the trade designation IRGACURE having product numbers 369, 651, and 961, all available from Ciba Geigy Chemicals, Hawthorne, N.Y.
If the binder precursor composition is to be cured by visible light radiation, a photoinitiator is required to initiate free radical polymerization. Examples of useful visible light photoinitiators can be found in U.S. Pat. No. 4,735,632. Preferably the catalysts are activated by photochemical means.
Optional Components
Optionally, the aminoplast resin/polyamide binder precursor compositions of the invention can further comprise an acrylamidomethyl-phenol resin (AMP). Preferably, the AMP would have a relatively low molecular weight (less than 500), an acrylamide functionality sufficient to provide crosslinking, and sufficient miscibility and viscosity with the oligomeric aminoplast resin and the polyamide so to form a compatible mixture as defined above. Specific AMPs and details of their manufacture are found in U.S. Pat. No. 4,903,440, the contents of which are incorporated herein by reference.
Any known and compatible additive useful in coatings in the abrasives art may be used as long as the amount of the additive used does not adversely affect the performance characteristics of the end-use product or article. Common additives include optically transparent fillers such as feldspar and silica, slip agents, and materials useful for dissipating static charges such as carbon black and graphite.
Backings
Useful backings of the invention may be comprised of cloth, vulcanized fiber, paper, nonwoven materials, fibrous reinforced thermoplastic backing, polymeric films, substrates containing hooked stems, looped fabrics, metal foils, mesh, foam backings, and transfer coated multilayer combinations thereof and are of the appropriate weight for the end use application.
The raw backings can be provided as woven fabrics using yarns composed of natural or synthetic fibers, as polymeric films, or as laminates of different types of polymeric materials, or as laminates of polymeric materials with non-polymeric materials. The woven polymeric fabrics may have different yarns in the warp and weft directions.
Cloth backings can be porous or sealed and they may be woven or stitch bonded. The cloth backing materials may also be surface treated using high pressure water (hydroenhanced) as described in U.S. Pat. No. 4,967,456, incorporated herein by reference. The effect of the water treatment is to increase the surface area of the yarns which provides a cloth that more readily and uniformly absorbs the desired chemical composition. Such cloths have a uniform surface finish and improved characteristics such as cover, abrasion resistance, drape, and reduced air permeability. The cloth backings may include fibers or yarns of cotton, polyester, rayon, lyocell, silk, nylon, or blends thereof. The yarns may be made of continuous filaments. The cloth backings can be provided as laminates with different backing materials described herein.
Examples of useful commercially available cloth backing materials include polyester fabrics woven with either spun yarns or continuous filament yarns, available from Milliken, Spartansburg, S.C.; and hydroenhanced polyester fabrics, available from Interspan Division of BBA Nonwovens, Fort Mill, S.C.
Paper backings can also be barrier coated, backsized, untreated, or fiber-reinforced. The paper backings also can be provided as laminates with a different type of backing material.
Nonwoven backings include spunbonded webs and laminates to different backing materials mentioned herein. Laminates may include those constructions having a network of filaments adhesively bonded or melt bonded to a nonwoven web. The nonwovens may be formed of cellulosic fibers, synthetic fibers, or blends thereof. Examples of commercially available nonwoven backing materials include TYPAR spunbonded polypropylene and REEMAY spunbonded polyester, available from Typar/Reemay, Old Hickory, Tenn., and STABILON scrims, available from Milliken. A xe2x80x9cscrimxe2x80x9d is defined as a fabric with an open construction used as a base fabric in the production of coated or laminated substrates.
The foam backing may be a natural sponge material or polyurethane foam and the like. The foam backing also can be laminated to a different type of backing material. The mesh backings can be made of polymeric or metal open-weave scrims. Additionally, the backing may be a spliceless belt such as that disclosed in U.S. Pat. No. 5,609,706, or a reinforced thermoplastic backing that is disclosed in U.S. Pat. No. 5,417,726, both incorporated by reference herein.
Preferred backing materials for use in the coated backings of the invention include cloth backings such as those woven from polyester, cotton, polyester/cotton, rayon, or lyocell yarns.
Preparation
The aminoplast resin/polyamide binder precursor may be prepared by mixing the various ingredients in a suitable vessel at an elevated temperature sufficient to liquefy the materials so that they may be efficiently mixed with stirring, but without thermally degrading them, until the components are thoroughly melt blended. This temperature depends in part upon the particular chemistry. For example, this temperature may range from about 30 to 150xc2x0 C., typically 50 to 140xc2x0 C., and preferably ranges from 90 to 125xc2x0 C. The components may be added simultaneously or sequentially, although it is preferred to first blend the oligomeric aminoplast resin and the thermoplastic polyamide component. Then, the catalysts are added followed by any optional additives including fillers. The binder precursor should be compatible in the uncured, melt phase. That is, there should preferably be no visible gross phase separation among the components before curing is initiated.
The aminoplast resin/polyamide binder precursor may be used directly after melt blending or may be packaged in pails, drums, or other suitable containers, as a solid or a powder, preferably in the absence of light, until ready for use. The binder precursors so packaged may be delivered to a hot melt applicator system with the use of pail unloaders, block melters equipped with rotating screws, and other solids feeding equipment. Alternatively, the hot melt binder precursors of the invention may be delivered to conventional bulk hot melt applicator and dispenser systems in the form of sticks, pellets, slugs, blocks, pillows, or billets. It is also feasible to incorporate organic solvent into the binder precursor; although this may not always be preferred.
It is also possible to provide the hot melt aminoplast resin/polyamide binder precursors of the invention as uncured, unsupported rolls of adhesive film. In this instance, the binder precursor is extruded, cast, or coated to form the film. Such films are useful in transfer coating the binder precursor to an abrasive article backing. It is desirable to roll up the film with a release liner (for example, silicone-coated Kraft paper), with subsequent packaging in a bag or other container that is not transparent to actinic radiation.
The hot melt binder precursors of the invention may be applied to the abrasive article backing by extrusion, gravure printing, coating, (for example, by using a coating die, a heated knife blade coater, a roll coater, a curtain coater, or a reverse roll coater), or transfer coating. When applying by any of these methods, it is preferred that the binder precursor be applied at a temperature of about 80 to 140xc2x0 C., more preferably from about 100 to 125xc2x0 C.
The hot melt aminoplast resin/polyamide binder precursors can be supplied as free standing, unsupported films that can be transfer coated to the backing and, if necessary, die cut to a predefined shape before transfer coating. Transfer coating temperatures and pressures are selected so as to minimize both degradation of the backing and bleed through of the binder precursor and may range from room temperature to about 120xc2x0 C. and about 30 to 1000 psi (0.03 to 1 kPa). A typical profile is to transfer coat at room temperature and about 400-500 psi (0.4 to 0.5 kPa). Transfer coating is a particularly preferred application method for use with highly porous backings.
It is also within the scope of this invention to coat the aminoplast resin/polyamide binder precursor as a 100 percent solids liquid, or from a solvent, although this method is not always preferred. A liquid binder precursor can be applied to the backing by any conventional technique such as roll coating, spray coating, die coating, knife coating, and the like. After coating the resulting binder precursor, it may be exposed to an energy source to activate the catalyst before the abrasive grains are embedded into the binder precursor. Alternatively, the abrasive grains may be coated immediately after the binder precursor is coated before partial cure is effected.
The coating weight of the hot melt aminoplast resin/polyamide binder precursor of the invention can vary depending on the grade of the abrasive particles to be used. In general, the application rate of the binder precursor composition of this invention (on a solvent free basis) is between about 4 to 500 g/m2, preferably between about 20 to about 300 g/m2.
Preferably, the hot melt aminoplast resin/polyamide binder precursor is applied to the abrasive article backing by any of the methods described above, and once so applied is exposed to an actinic, preferably UV, energy source to initiate at least partial cure of the photosensitive materials. The partial curing facilitates further processing, web handling, and prevents the coated side of the backing from sticking to the backside of the backing when the coated backing is in the form of a roll. Final cure may be completed by further processing with an additional energy source, typically thermal energy.
Curing of the hot melt aminoplast resin/polyamide binder precursor begins upon exposure of the binder precursor to an appropriate energy source and continues for a period of time thereafter. The energy source is selected for the desired processing conditions and to appropriately activate the chosen photoactive catalyst system. The energy may be actinic (for example, radiation having a wavelength in the ultraviolet or visible region of the spectrum), accelerated particles (for example, electron beam radiation), or thermal (for example, heat or infrared radiation). Preferably, the energy is actinic radiation.
Suitable sources of actinic radiation include mercury, xenon, carbon arc, tungsten filament lamps, sunlight, and so forth. Ultraviolet radiation, especially from a medium pressure mercury arc lamp, is preferred. Exposure times may be from less than about 1 second to 10 minutes or more (to preferably provide a total energy exposure from about 0.1 to about 10 Joule/square centimeter (J/cm2) depending upon both the amount and the type of reactants involved, the energy source, web speed, the distance from the energy source, and the thickness of the binder precursor to be cured.
The aminoplast resins/polyamide binder precursors may also be cured by exposure to electron beam radiation. The dosage necessary is generally from less than 1 megarad to 100 megarads or more. The rate of curing may tend to increase with increasing amounts of photocatalyst and/or photoinitiator at a given energy exposure or by use of electron beam energy with no photoinitiator. The rate of curing also tends to increase with increased energy intensity.
Treated Hydroenhanced Backing Substrates
The present invention also provides treated backing substrates comprising a backing comprising hydroenhanced cloth and a treatment coat on said backing. The type of cloth that may be hydroenhanced is not limited and may be any type of cloth having the properties required for application in an abrasive article. Such properties include sufficient weight, texture, density, weave, heat, and chemical resistance, etc. Preferred hydroenhanced cloths include those made from polyester, cotton, lyocell, rayon, and polycotton yarns. More preferred hydroenhanced cloths are made from polyester yarns.
The type of treatment coat used on hydroenhanced cloth backing substrates is not limited. The treatment coats may be melt processable, or solvent borne, waterborne or 100 percent solids, and radiation or heat curable. Useful treatment coats for the hydroenhanced backing substrate include those comprising phenolic resins, novolak resins, nitrile latex resins, aminoplast resins having pendant, xcex1,xcex2-unsaturated carbonyl groups, urethane resins, epoxy resins, urea-aldehyde resins, isocyanurate resins, melamine-aldehyde resins, acrylate resins, acrylated isocyanurate resins, acrylated urethane resins, acrylated epoxy resins, bismaleimide resins, polyester resins, and aminoplast resin/thermoplastic polyamide blends as described herein, acrylated oligomer/thermoplastic polyamide blends (as described in copending and co-assigned application Ser. No. 09/219,289, filed Dec. 22, 1998, entitled xe2x80x9cAcrylated Oligomer/Thermoplastic Polyamide Presize Coatings for Abrasive Article Backings,xe2x80x9d incorporated by reference herein, and mixtures thereof. Preferred treatment coatings comprise melt processable aminoplast resin/thermoplastic polyamide blends and phenolic resins.
The treatment coats for the hydroenhanced backing substrate may also contain a catalyst, photoiniator, or thermal initiator as described above and is known in the art. Such treatment coats may also contain other known and conventional additives such as solvents, fillers, viscosity modifiers, and the like.
The treated hydroenhanced substrates may be prepared by methods listed above and other known conventional methods. The range of coating weights for the treatment coat is the same as described above for the aminoplast resin/polyamide compositions. The treated backing substrates can be used alone or may be a layer in a multilayer substrate made by transfer coating or other known means.
Hydroenhanced cloth backing substrates provide surprisingly improved adhesion to treatment coats and greatly improved flexibility when compared to non-hydroenhanced cloth of the same type.
Objects and advantages of this invention are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention.